1. Field of the Invention
The present invention relates generally to vehicle air-conditioning systems, and more particularly to a system with electric heating devices integrated into the system heat exchanger as an auxiliary heat source for more rapidly heating engine cooling water used to heat a passenger compartment.
2. Description of Related Art
In recent years, as vehicle engines have become more efficient, there has been a tendency for the temperature of warmed vehicle engine cooling water to remain at a lower temperature than in the past, even after the engine has warmed up. Consequently, in warm water type air-conditioning systems for heating the inside of a passenger compartment, insufficient heating capacity has been become a problem.
German Patent Application No. 4433814A1 discloses a system wherein electric heating devices are mounted between pairs of warm water tubes, or between water tubes and radiating fins, in a warm water type heat exchanger. Heat produced by the heating devices is used to heat warm water inside the tubes.
However, in the above system, because the electric heating devices are mounted in direct contact with the warm water tubes, and heat from the electric heating devices is directly conducted to the warm water inside the tubes, the amount of heat transferred from the electric heating devices to the heating air is minimal, and the proportion of the air heated by the electric heating devices is low.